Method and apparatus for forming no-strip wire connection



Feb. 24, 1970 A. F. swANsclJN 3,497,607

FOR O Filed April 12, 1968 Mlm if V/ United States Patent O U.S. Cl. 174-87 5 Claims ABSTRACT OF THE DISCLOSURE The method and apparatus for forming an electrical connection between wire ends in which at least one wire has an insulated surface. A tapered helical spring is provided With cutting means on its radial inner margin to cut through the insulation and make an electrical circuit between adjacent wires so that a connection may be completed without the necessity of removing the insulation.

SUMMARY OF THE INVENTION This invention relates to screw-on connectors for electrical wires and more particularly relates to a method and apparatus for providing a secure no-strip electrical connection for a plurality of 'wire conductors.

It is an object of this invention to provide a method for forming an electrical connection between the ends of wire conductors with a screw-on type connector assembly.

Another object is to provide a method for electrically connecting a plurality of wire conductors, one or more of which are insulated, in which it is not necessary to strip the insulated wire ends prior to making the connection.

Another important object is to provide a method of forming an electrical connection between wire conductor ends, one or more of which are insulated, in which cutting means are provided in the connector to cut through the insulation into electrical contact with the conductor as the connection is formed.

Another important object is to provide a method and apparatus for forming an electrical connection between Iwire ends, one or more of which are insulated, in which a helical spring element in the connector cuts through the insulation into contact with the conductors to form an electrical circuit between adjacent conductors.

Still another object is to provide a method and apparatus for forming an electrical connection between a plurality of wires, one or more of which'is insulated, in which a helical spring within a connector shell is formed with a throat section of narrowed pitch diameter to resiliently bear against and cut through the insulation as the connector is turned onto the wires.

Yet another object is to provide a method and apparatus for forming an electrical connection between insulated Wire ends in which a helical spring within a connector shell is formed with its radical inner margin having a serrated edge so that a's the connector is turned onto the wires the edge will tear through the insulation and the spring will provide an electrical circuit between adjacent wires.

These and other objects of the invention Will become apparent to those skilled in the art when the following specification is read in conjunction with the accompanying drawings.

3,497,607 Patented Feb. 24, 1970 FIGURE l is an axial section of a wire connector embodying features of the invention, shown prior to making an electrical connection;

FIGURE 2 is a view similar to FIGURE 1 illustrating the connector after connecting together a pair of wire conductors;

FIGURE 3 is an enlarged cross sectional View taken along line 3-3 of FIGURE 2, with the cap removed;

FIGURE 4 is an enlarged View, partially in cross section, of a portion of the connector of FIGURE 2;

FIGURE 5 is a partial view of a modified helical spring element.

DETAILED DESCRIPTION Referring now to the dra'wings and particularly FIG- URE 1 a screw-on type connector for forming a no-strip connection is illustrated generally at 10. Connector 10 is used to form an electrical connection between the ends of two or more wire conductors, as for example 12 and 14. The method and apparatus of this invention would be used where it is desirable to quickly connect wire ends together without the necessity of stripping insulation from the wires. The invention works Well with conductors having a relatively thin insulation, such as a coating of enamel or similar type of dielectric material which may be baked on or otherwise applied to the wire surface. Bell wire and wire having a tough coating of material, such as that sold under the trademark Teflon, may be used but it is understood that the invention can be used with many other types of insulated wire. The invention will find application in electrically connecting 2, 3 and in many cases 4 wires in any combination of size or wire type. Thus, an enamel insulated wire may be joined with the stripped end of a heavier insulated wire, a plurality of enameled wires of different diameters may be joined, yor one or more insulated Wire ends may be joined with stripped stranded |wires.

Several approaches are possible: the connector may be a helical spring with its two ends of equal diameter and a smaller diameter section near its center length, or the one end diameter may be larger than the opposite end. The connector can be applied to the wires by means of a suitable driving tool. Where a bare spring is driven on the wires the resulting connection may then be insulated by suitable means such as tape. Alternatively, the spring may be driven `by a shell or cap, such as that of connector 10 which itself acts as the insulating covering.

Connector 10 comprises an open-ended shell or cap 16 having an internal bore or cavity 18 and a helical spring 20 mounted within the cavity. Shell 1-6 may be made from a suitable dielectric material which is tough, durable, and has sufficient rigidity to retain the spring Within the cavity. Suitable classes of thermo-set or thermo-plastic materials can be used.

The external surface of shell 16 is formed with a plurality of longitudinal ribs 22 which act as a gripping surface to manually turn the connector onto the wires. A generally circular skirt 24, which preferably is formed integral with the body of shell 16, extends outwardly from the cavity and acts both as a guide for receiving the wires and as a shield to prevent arcing so that the connector can be used in both high and low voltage applications. The outer end of the cavity is formed with internal thread detail 26 While the inner end is formed with internal 3 thread detail 28. Threads 26 and 28 function to hold the spring and wire ends against axial movement While threads 28 additionally guide the spring into the bottom of the cavity. The invention contemplates that other spring retaining means, such as a shoulder at the outer end of the cavity, may also be used with this invention.

Spring 20 is formed with a tapering configuration such that its intermediate turns form a throat section 30 of -decreased pitch diameter. One or more of the spring turns are expanded on a coil forming machine to an increased pitch diameter at 32, which will be referred to as the small end of the spring, for engagement with threads 28. The other end of the spring is formed with its turns having a larger pitch diameter at 34, which will be referred to as the large end of the spring, for engagement with threads 26. With spring 20 assembled within cavity 18 an annular space 36 will remain 'between the spring and cavity. The spring will expand into this space toa greater or lesser extent, depending upon the size and number of wires used, when the connector is turned onto the wires.

As shown in FIGURE 2 end wall 38 of the shell may be provided with a conical abutment 40- extending a short distance into the cavity. Abutment 40 functions to guide or cam the sharp ends of wires 12 and 14 outwardly as they are advanced through the small end of the spring. This tends to prevent the wire ends from penetrating through the shell end, as may occur if one of the wire ends is positioned so that it overlaps the other wires in an axial direction.

A shoulder 42 may be provided within the cavity to abut against the end of the last turn at the small end of the spring. This functions to drive the spring onto the wires by preventing rotation of the spring relative to shell 16 as the connection is being made. It is contemplated that other suitable means, such as a metal disc inserted within the cavity, maybe used to drive the spring.

Spring 20 is formed with a cross sectional shape defining a cutting edge on its radial internal margin, as at 44 in FIGURE 4. The cross sectional shape of the preferred embodiment is illustrated as diamond-shaped, but it is understood that other shapes, such as round, tear- -drop, channel or rectangular may also be used. The cutting edge 44 moves with a knife-like abrading action against insulation coating 46 of the wire as the connection is being made. The cutting edge will move through the insulation and then cut, abrade or gouge into the metal of conductor 48. Since the outer surfaces of both wires 12 and 14 are cut in this manner, an eective electrical circuit or bridge is established between the conductors, as illustrated in FIGURE 3, even though no electrical oontact is made at the wire interface. Accordingly, spring 20 is fabricated from a material having electrical conductivity properties, and yet having suitable resiliency and strength. A desirable material for the spring would be steel, although it is understood that the invention is not thus limited.

A modied spring 50 for use with the invention is illustrated in FIGURE 5. The radial inner margin of spring 50 is formed with a serrated or toothed cutting edge 52. Serrated edge 52 provides a sawing action against the insulation of the wires during the connection operation. This type of cutting edge will more readily cut through insulation which is particularly tough or hard.

Cutting edge 44 of the spring is formed so that it projects against the surface of the wires with a minimum of axial canting. This insures that a good cut is made through the insulation and into the conductor material to establish good electrical contact.

The method of forming the electrical connection for the wires is as follows:

Two or more conductor wires 12 and 14, at least one of which has a coating of relatively thin insulation, are positioned with their end sections together as illustrated in FIGURE 1. Spring 20 is then driven onto this cluster of wires by a suitable driving tool, such as connector y10. Connector is rst positioned over the wire end sections, which are inserted within spring 40. The connector or tool is then rotated or turned in a clock-wise direction, as viewed from end 38, so that spring 20 is driven or screwed onto the wires. The intermediate turns at throat 30 iirst engage the wires, with cutting edge 44 moving against the insulation in a cutting action. Since the combined outer diameter of the two wires is larger than the internal diameter of throat section 30 when the spring is free, the throat section turns will expand outwardly into space 35. The resiliency of the spring will correspondingly exert a compressive force against the wires to assist in the cutting action. As throat section 30 expands the effective length of spring 20 will shorten. To compensate for this the turns at large end 34 will move backwards through threads 26, `depending on the amount of spring expansion. A sufficient number of large end turns are provided to engage these threads so that an adequate holding force remains after such expansion.

Continued turning of connector 10 relative to the wires will advance the wires through the throat sections against abutment 40. During this action, additional spring turns will move into engagement with the wires due to the expanding action of the throat section. The more turns which engage with the wires, the better the resulting electrical connection.

As cutting edge 44 cuts through the insulation continued turning of the connector will result in a cutting or gouging action against the underlying metal of conductor 48. This provides intimate metal-to-metal contact between the spring and conductor material so that an electrical circuit or bridge is established along the length of the spring turns between adjacent wires. The resilient compressive force of throat section 30 against the wires will assist in maintaining this electrical contact, even if the connection is subjected to vibration or shock forces.

Where the driving tool is of the type which is removed after the connection is made, insulating tape then may be wrapped around the spring and wire cluster.

In view of the foregoing description it is clear that applicant has provided herein a new and improved method and apparatus for making an electrical connection between a plurality of wires, one or more of which has a thin coating of insulation. A connection is made rapidly using a simple connector assembly without the necessity of stripping insulation from the wire. The resulting connection will securely hold together and yet provide good electrical contact since the connector spring itself serves as the conducting element. Moreover, the invention improves on the crimp type of connectors since it is not necessary to precisely orient the wires prior to making the connection.

I claim:

1. Apparatus for electrically connecting together end sections of conducting wires, in which at least one wire has an insulation coating, comprising the combination of: a connector shell having an open-ended cavity; a helical spring positioned in the cavity with intermediate spring turns defining a narrowed throat section for receiving the wire end sections; cutting means formed on the radial inner margin of the spring to cut through the insulation and electrically contact adjacent conductors to form a current carrying circuit therebetween, the cutting means comprlsing a cutting edge having a plurality of radially inwardly extending serrations spaced along the edge of the spring to saw the insulation away as the connector is turned onto the wires.

2. The apparatus of claim 1 and further including means to transmit torque to the spring for turning the sarneonto the wires.

3. The invention of claim 2 and further characterized in that the means to transmit the torque comprises a shoulder formed within the shell cavity and extending into abutting relationship with the free end of the spring Within the cavity.

4. The invention of claim 1 and further characterized in that the serrations comprise a series of teeth disposed 6 along the cutting edge of at least the narrowed throat 2,490,809 12/ 1949 Holke 174-94 XR section of the spring. 3,075,038 1/1963 Schinske 174-87 5. The invention of claim 4 and further characterized 3,156,762 11/1964 Matthysse 174-87 n that each of said teeth are formed by notches in the cutting edge having surfaces disposed transversely of the DARRELL L. CLAY, Primary Examiner spring cross section. 5 l

U.S. Cl. X.R. References Cited UNITED STATES PATENTS 1,933,555 1l/1933 Jasper 174-87 10 

